(1) Field of the Invention
The present invention pertains to the construction of an electromagnetic device, such as an electric motor or electric generator, where component parts of the electromagnetic device have been redesigned to significantly reduce its size.
(2) Description of the Related Art
Current trends in the design of electromagnetic machines such as motors have lead to compact designs of high efficiency motors. The motor designs have obtained high power to weight and high power to size ratios through their use of high magnetic flux density magnets on their rotors and high density windings on their stators.
Compact high efficiency motors are constructed of basically the same component parts of larger motors, those being a casing or housing shell containing the stator, a pair of end shields attached to opposite ends of the stator, and a rotor supported for rotation in the stator bore by a pair of bearings mounted in the end shields.
In the reduction in size of these high efficiency motors the surface areas of motor component parts available for use in establishing secure connections between the component parts is also reduced. For example, in the construction of a larger motor there are typically substantial areas on interfacing surfaces of motor component parts, such as a stator and an end shield, to accommodate connectors such as nut and bolt connectors to securely hold the two component parts together. With the ample areas available on the interfacing surfaces of the component parts, larger connectors may be employed to securely hold the component parts together. However, when the motor is significantly reduced in size, all of its component parts are reduced including the interfacing surfaces of mating component parts and the connectors employed in securely holding the component parts together. In reduced size motors, the component parts must be redesigned in order to provide the needed secure connections between the component parts.
A reduction in motor size also requires positioning all of the motor component parts closer together. This includes the electrical component parts of the motor such as the stator winding, and the structural component parts of the motor such as the end shields. Reduced motor size brings the end shields much closer to the end turns of the stator winding presenting the undesirable possibility of arcing or shorting of the stator winding with the metal end shields. The reduction in size bringing component parts closer together also presents the problem of heat generated in one area of the motor adversely affecting another area of the motor, for example, the electronics of the motor. The component parts of the reduced size motor must be redesigned to avoid the potential problems of shorting and heat affecting motor performance.
The present invention is an electromagnetic device, such as a motor, having component parts that are assembled together to provide a motor of compact size having high efficiency. The novel features of the invention are in the constructions of the component parts and, although described as applied to a motor, they may also be applied to alternators and generators.
The motor of the invention is basically comprised of a stator containing the stator winding, a pair of end caps attached to axially opposite ends of the stator and insulating the end turns of the stator winding from the metal laminations of the stator, an insulator attached over one of the end caps, a pair of end shields, one attached over the end cap at one end of the stator and the other attached over the insulator at the opposite end of the stator, and a rotor. The novel features of the motor are primarily in its component parts assembled at the axially opposite ends of the stator. Therefore, the stator construction and rotor construction are described in only general terms with it being understood that alternative stator and rotor constructions may be employed with the invention.
The stator is comprised of a stack of individual stator laminations with each lamination having a generally octagonal peripheral edge and a plurality of stator poles extending radially inwardly toward a center bore of the laminate as is typical in many stator constructions. However, the octagonal shape of the peripheral edge is one of the novel features of the motor construction that contributes to the secure connection of the motor""s component parts. With the stator laminates arranged in a stator stack, the exterior surface of the stator stack is octagonal and includes four spatially arranged pairs of flat surfaces separated by a semi-circular trough. The four pairs of flat surfaces and their middle troughs extend axially over the exterior surface of the stator stack between longitudinally opposite first and second end surfaces of the stator stack.
The first and second end caps are assembled over the opposite first and second end surfaces of the stator stack. Each end cap is constructed of an insulating material and includes a plurality of posts radiating inwardly toward a center bore of the cap. The posts are configured complimentary to the poles of the stator laminations and overlay the stator poles at the axially opposite ends of the stator. The end turns of the stator winding are wrapped around each of the end cap posts and in this manner the posts insulate the end turns from the metal of the stator poles. In addition, the first end cap at the first end of the stator has a spacer projecting therefrom. The spacer projects longitudinally and axially outwardly from the first end cap beyond the stator end turns wrapped around the posts of the first end cap. The spacer engages against the first end shield attached to the stator stack over the first end cap and thereby spaces the metal of the end shield from the turns in the stator winding ensuring that a short will not occur between the first end shield and the stator winding.
Thus second end cap, like the first end cap, is constructed of an insulating material and also includes inwardly radiating posts. End turns in the stator winding at the second end of the stator are wrapped around the posts of the second end cap in a conventional manner. In addition, the second end cap has supports for male terminal connectors that are connected to electrical leads of the stator winding. The supports project longitudinally and axially outwardly from the second end cap and securely hold the male electric terminals in a desired orientation that facilitates the assembly of the motor component parts.
The insulator is attached over the second end cap and the second end of the stator stack. The insulator is constructed of an electrically insulating and thermally insulating material. Its construction covers over the end turns of the stator winding at the second end of the stator and thereby insulates the end turns from the metal of the second end shield attached to the second end of the stator. In addition, the insulator thermally insulates any electronic components used in association with the motor and attached to the second end shield from the heat generated in the stator. The insulator is also formed with tubular lead guides corresponding to each of the male electric terminals supported by the second end cap. The tubular lead guides project longitudinally and axially outwardly from the insulator and surround each of the male terminals supported by the second end cap.
The second end shield is constructed with lead openings corresponding to the number of male terminals supported by the second end cap and the number of tubular lead guides on the insulator surrounding the terminals. The lead openings in the second end shield are positioned so that the tubular lead guides will pass through the openings and in this manner the tubular lead guides of the insulator also insulate the electric terminals of the stator from the metal of the second end shield. The tubular lead guides also positively position the male electric terminals of the stator relative to the second end shield so that they can easily be connected with female electric connectors of an electronics package associated with the motor as it is connected to the second end shield.
Both the first and second end shields are formed with generally square peripheral configurations and with four columns projecting longitudinally from the four corners of their square configurations. Each of the four columns of the end shields is formed with a flat base surface that mates against one of the first and second end surfaces of the stator stack. In addition, adjacent the base surfaces of the columns, shoulders project longitudinally outwardly from the base surfaces. The shoulders are formed with shoulder surfaces that overlie the pairs of flat surfaces on the exterior surface of the stator stack. The engagement of the column shoulder surfaces over the flat surfaces on the exterior of the stator stack securely holds the first and second end shields to the opposite first and second end surfaces of the stator stack preventing relative torsional or radial movement between the end shields and the stator stack.
With the design of the component parts of the electric motor described above, the size of the motor can be significantly reduced while avoiding the potential problems of securely connecting component parts of the motor together and insulating, both electrically and thermally, the electrical component parts of the motor from structural component parts.